It's not a misuse; evidently it's a new use.
The Oxford English Dictonary, since September of 2011 has included this definition of literally:
"Used for emphasis or to express strong feeling while not being literally true: I have received literally thousands of letters.'"
That doesn't prove it's a correct use. It proves that even The Oxford English Dictionary
is not always right.
I think you misunderstand: the OED
, not prescriptive